The present invention is directed to a submersible pump for producing fluid from well intersecting a producing formation, preferably a hydrocarbon-producing formation, and more particularly is directed to an apparatus for producing fluid from a well and for limiting the accumulation of sediment in wells in which the formation produces solids along with the production fluids.
It is well known that in producing oil and/or gas wells, the fluid in the well may be elevated to the surface by utilizing a pump installed in the well. One type of pump that is often utilized is an electric submersible pump. Electric submersible pumps may be used for a variety of reasons, such as for example in wells where artificial lift is required when formation intersected by the well does not provide the necessary lift to produce the fluid to the surface.
Electric submersible pumps, depending upon the application, are often deployed in wells with open rat holes. That is, the pumps are deployed in wells which have casing cemented in a wellbore to a certain depth and wherein the wellbore is drilled to a greater depth so that there is an uncased, or open rat hole below the casing. In some formations intersected by the well, the fluid produced therefrom will contain solids. The solids tend to get deposited in the rat hole, and over time the deposits, also referred to as sediment, can cause production problems such as reduced well productivity, and cause equipment problems, such as motor overheating. If the electric submersible pump system is deployed in the well below the perforations in the casing through which the formation fluid is communicated into the well, there may be insufficient flow of fluid around the motor in the electric submersible pumping system to cool the motor.
When an electric submersible pump is placed above the perforations, flowing well fluid will produce some motor cooling. When the system is placed below casing perforations, the motor in the electric submersible pumping system is generally not exposed to flowing well fluid. Thus, there is a need for a method and apparatus for limiting the accumulation of sediments in a rat hole and for providing cooling to a motor used in an electric submersible pumping system when the system is placed below perforations in a well.
The present invention provides a method and apparatus for producing fluid from a well, for limiting the accumulation of sediments in the well, and for providing cooling to motors used in electric submersible pump systems when the system is placed below perforations in the well. The apparatus comprises an electric submersible pumping system lowered into a well on a production tubing. The electric submersible pumping system includes a submersible production pump, a seal section connected to a lower end of the pump, and a submersible motor connected to the seal section for driving the production pump. A production pump intake is positioned at or near the lower end of the production pump above the seal section. A submersible auxiliary pump is connected below the motor. The auxiliary pump has an auxiliary pump intake at or near a lower end thereof, and includes an auxiliary pump discharge positioned between the submersible motor and the auxiliary pump. The auxiliary pump discharge is designed such that the motor is effectively sealed from the auxiliary pump discharge to prevent fluid from the auxiliary pump from being pumped or discharged into the submersible motor. The auxiliary pump discharge has at least one and preferably has a plurality of discharge ports.
The production tubing preferably has a sufficient length so that the electric submersible pumping system is located in the well below the perforations that communicate the producing formation with the interior of the well. Fluid from the well will be drawn in through the auxiliary pump intake, will be pumped upwardly through the auxiliary pump discharge and then upwardly in the well above the submersible motor, which drives both the production pump and the auxiliary pump. In wells where the producing formation produces sediment along with the fluid, some of the sediment that will naturally flow downward in the well due to gravity will be drawn in through the auxiliary pump intake and will be pumped upwardly in the well along with the fluid pumped by the auxiliary pump.
The apparatus preferably includes at least one and preferably a plurality of discharge tubes or discharge tubings connected at a lower end to the auxiliary pump discharge. The discharge tubes extend upwardly in the well past the submersible motor. The tubes may extend upwardly past the production pump intake and may expel the fluid and sediments pumped upwardly therethrough into the interior of the well above the production pump intake. A portion of the fluid expelled from the discharge tubes along with a portion of the sediment will flow downwardly in the well. A portion of the fluid expelled from the discharge tubes along with a portion of the sediment will be taken in through the production pump intake and will, along with other fluid from the well, be produced upwardly by the production pump through the production tubing on which the system is lowered. In a separate embodiment, the upper ends of the discharge tubes may be communicated directly to the production pump intake so that all of the fluid and sediment taken in and pumped upwardly through the discharge tubes by the auxiliary pump will be received in the production pump intake and will be produced upwardly by the production pump through the production tubing. Because the auxiliary pump will pump sediments upwardly so that some sediment can be produced upwardly through the production tubing, the invention limits the accumulation of sediment in the well.
In addition to limiting the accumulation of sediment in the well the present invention provides a method and apparatus for cooling the submersible motor in an electric submersible pumping system when the system is placed below perforations in the well. The auxiliary pump of the present invention pumps fluid upwardly in the well which allows for downward flow of fluid in the well past the motor. The auxiliary pump preferably pumps fluid upwardly at a rate sufficient to create a downward flow in the well of preferably at least about 1 ft/second past the motor, so that the downward flow will provide efficient motor cooling.
It is therefore an object of this invention to provide a method for producing well fluid from a well in which the producing formation produces sediments along with fluid, and for limiting the accumulation of the sediments in the well. It is a further object of the invention to provide a method for producing fluid from a well in which the pumping system is located below the perforations and for cooling the motor utilized in the pumping system.